Steering columns for vehicles are provided with tilt mechanisms which allow vertical position adjustment of the steering wheel to allow the driver to assume a preferable driving position. For the same purpose, they can be provided with telescopic mechanisms, which allow position adjustment of the steering wheel in forward/backward direction, or tilt-telescopic mechanisms, which allow position adjustment in both vertical and forward/backward direction.
In order to enable tilt rotation of the tilt mechanism around the tilt pivot or telescopic sliding along the steering column axis direction, the steering column is configured so that it can be fastened to vehicle side supporting members in order to maintain the secured state of the steering column in the selected position, while at the same time allowing a relative displacement with respect to the vehicle side supporting members.
In order to perform the relative displacement and securing of the steering column with respect to the vehicle side supporting members, distance brackets, which are provided with, for example, flat side walls, are used as column side supporting members, which are anchored to the cylindrical steering column. Typically, the side walls of these distance brackets are perforated with round holes or long holes, with a shaft rod member passing through the round holes in the tilt mechanism and through the long holes in the telescopic mechanism, enabling tilt rotation around the tilt pivot or telescopic sliding along the axis of the steering column. The steering column and the distance brackets are members which are manufactured separately, and are generally anchored to each other by welding.
Now, a novel steering column has been proposed, which does not use these distance brackets anchored by welding. Instead, a portion of the tubular material is replaced by a bulge portion that is bulged out therefrom, which can be manufactured using a hydraulic bulging method. Among the steering columns of this type, a steering column is known, in which, as shown in FIG. 11, for example one portion of the steering column 51 is bulged out to form a bulge portion 52.
The bulge portion 52 is provided with a pair of back-to-back flat surface portions 53, which directly abut against the vehicle side supporting members (not shown in the drawings). These flat surface portions 53 are perforated by round holes 54 in order to pass the shaft rod member through. With this steering column 51 in which the bulge portion 52 is formed, it is possible for example to omit some of the parts constituting the tilt mechanism, which has the advantage that is allows a reduction of manufacturing costs for the steering device, for example.
The following prior art document is related to the invention of the present application:
Japanese Laid-Open Patent Publication, JP H8-276852A (page 3, FIG. 3)
However, when manufacturing using a hydraulic bulging method, a pressure force accompanying the punch perforations acts on the flat surface portions 53, particularly when perforating the round holes 54, causing a certain amount of deviation around the hole portions in the flat surface portions 53, which may prevent the flat surface portions 53 from being finished to flat surfaces. In other words, with the hydraulic bulging method, instead of countering the cutting load with a die as during the punching process in a press method, the goal is to counter that load with pressure oil O, which is a non-rigid body in contact with a workpiece W opposite the applied pressure of a punch P, as shown in FIG. 12. In this case, while there are no problems with the perforations themselves, the flat surfaces 53 warp around the perforated portions, resulting in, the flat portions 53 not being finished as flat surfaces.
The warping which arises on the flat portions 53 creates, an error equal to ΔD with respect to a reference plane I, as shown in FIG. 13 for example. If this warping on the flat surface portions 53 becomes large, the contact surfaces become unstable during tilt or telescopic adjustment operations, preventing the intended fastening power from being achieved and the steering column from being held securely.
An object of the present invention is to provide a positioning type steering column device which can prevent a drop in the fastening grip of the steering column, even if warping arises during punched perforation when forming a bulge portion of the steering column using a hydraulic bulging method.